Formula NaIO4 Melting point 300 °C Appearance white crystals | Molar mass 213.8918 g/mol Density 3.86 g/cm³ | |
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Sodium periodate
Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates it can exist in two different forms: sodium metaperiodate, which has the formula NaIO4, and sodium orthoperiodate, normally this means sodium hydrogen periodate (Na2H3IO6) but the fully reacted sodium orthoperiodate salt, Na5IO6, can also be prepared. Both salts are useful oxidising agents.
Contents
Preparation
Classically, periodate was most commonly produced in the form of sodium hydrogen periodate (Na3H2IO6). This is commercially available, but can also be produced by the oxidation of iodates with chlorine and sodium hydroxide. Or, similarly, from iodides by oxidation with bromine and sodium hydroxide:
NaIO3 + Cl2 + 4 NaOH → Na3H2IO6 + 2 NaCl + H2O NaI + 4 Br2 + 10 NaOH → Na3H2IO6 + 8 NaBr + 4 H2OModern industrial scale production involves the electrochemical oxidation of iodates, on a PbO2 anode, with the following standard electrode potential:
H5IO6 + H+ + 2 e− → IO−3 + 3 H2O E° = 1.6 V
Sodium metaperiodate can be prepared by the dehydration of sodium hydrogen periodate with nitric acid.
Na3H2IO6 + 2 HNO3 → NaIO4 + 2 NaNO3 + 2 H2OStructure
Sodium metaperiodate (NaIO4) forms tetragonal crystals (space group I41/a) consisting of slightly distorted IO−
4 ions with average I–O bond distances of 1.775 Å; the Na+ ions are surrounded by 8 oxygen atoms at distances of 2.54 and 2.60 Å.
Sodium hydrogen periodate (Na2H3IO6) forms orthorhombic crystals (space group Pnnm). Iodine and sodium atoms are both surrounded by an octahedral arraigement of 6 oxygen atoms; however the NaO6 octahedron is strongly distorted. IO6 and NaO6 groups are linked via common vertices and edges.
Powder diffraction indicates that Na5IO6 crystallises in the monoclinic system (space group C2/m).
Uses
Sodium periodate can be used in solution to open saccharide rings between vicinal diols leaving two aldehyde groups. This process is often used in labeling saccharides with fluorescent molecules or other tags such as biotin. Because the process requires vicinal diols, periodate oxidation is often used to selectively label the 3′-termini of RNA (ribose has vicinal diols) instead of DNA as deoxyribose does not have vicinal diols.
NaIO4 is used in organic chemistry to cleave diols to produce two aldehydes.
In 2013 the US Army announced that it would replace environmentally harmful chemicals barium nitrate and potassium perchlorate with sodium metaperiodate for use in their tracer ammunition.